Historically, many different types of sleep units have been utilized. Such sleep units have varied from crude piles of straw laid on the ground to sophisticated structures involving complicated spring mechanisms.
In designing a sleep unit, it is desired to provide a degree of softness for the user while at the same time preventing undue deflection of the sleep unit which may result in the heavier torso portion of the body sinking deeper into the sleep unit than the legs and above shoulder regions of the body. It is also desired to prevent bottoming out of the sleep unit which may occur when the user is a large, heavy person.
One of the most common sleep units in use is a structure in which a box spring is supported in a bed frame. A mattress overlies the box spring. Usually the mattress is also provided with springs. Such a construction has proved generally satisfactory. However, the conventional structure is relatively expensive because two sets of springs are normally employed.
In accordance with the present invention, a single set of springs is utilized. The springs are of a curved leaf-type construction. In use, the spring resistance increases with deflection. This prevents undue deflection of the springs which are under the torso portion of a person's body. This spring construction also tends to prevent bottoming out.